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Rock Snot - Coming to a River Near You

Have you been concerned about didymo (a.k.a. "rock snot"), the algae that seems to be slowly taking over waterways throughout the northeast? A study from the University of New Brunswick, recently published in the Canadian Journal of Fisheries and Aquatic Sciences, offers both good news and bad news about didymo’s spread.

Didymosphenia geminata is an algae (technically, a diatom) that forms a dense mat on the bottom of swiftly flowing freshwater rivers and streams. As its nickname implies, it looks a bit like a thick, gooey layer of mucous covering the bottom of streams and rivers. It can smother other aquatic vegetation, reducing habitat for the aquatic macroinvertebrates that fish feed on. In the past two decades it has been identified in the waters of the U.S., Canada, New Zealand and Europe.

First, the good news. Especially for anglers and boaters. Up until now, the conventional wisdom was that didymo was an exotic invasive algae species that was hitchhiking between watersheds on anglers’ gear, especially felt-soled wading boots, and on boats. State environmental agencies have launched intensive educational campaignsurging anglers and boaters to wash their gear and let it dry thoroughly to prevent further spread of didymo. Washing gear with a bleach solution was recommended. But according to the University of New Brunswick study, anglers and boaters are not spreading anything that was not already in their local ecosystems. So if anglers and boaters are not to blame for the ooze of algae popping up in more and more watersheds, what is going on? Sit tight for the bad news.

The didymo study looked at archival samples of lake sediment from several regions in Canada, and they found that didymo has been in these ecosystems for quite some time. Evidence of didymo can be found in the sediment record back to the beginning of the 20th century and possibly even the last decade of the 19th century. The researchers found that even in ecosystems which did not necessarily have evidence of didymo, there were increases in other algae species at approximately the same rate that didymo was increasing in lakes where it was present. The researchers found that increases in didymo and other algaes appeared to correlate with the warming climate. The study leader, Michelle Lavery, said, "We can't make any solid claims as to what the mechanism is that is favoring didymo, but we strongly suspect it has to do with climate." So although anglers and boaters seem to be off the hook for spreading didymo, the awakening of dormant didymo in bodies of water potentially throughout North America by a gradually warming mean global temperature would mean that we have little hope of preventing didymo from appearing in a river near you. That’s the bad news.

So does this new view of didymo mean that anglers and boaters don’t need to sweat about washing down their gear between destinations? No. There are other aquatic nuisance species that are much better understood than didymo that can hitchhike on our gear. Zebra mussels are one prominent example. So keep scrubbing down between trips.

I think the take-away message from this study is that didymo is still going to be a concern for those of us who rely on healthy and diverse waterways for our outdoor recreational fix. Although the indication is that anglers and boaters are not spreading it, this new study suggests that didymo may continue to appear throughout the waterways of the traditionally cooler regions of North America as long as the mean global temperature continues to inch up. I suspect that these findings mean that researchers can now focus their future didymo studies looking for ways to minimize inevitable didymo blooms under the assumption that it is already present but dormant in most aquatic ecosystems. And for anglers who will have to adapt to wading through dense patches of slippery rock snot? Maybe it’s time to invest in a wading staff.